The present invention is directed to bicycles and, more particularly, to an apparatus for detecting rotation of a bicycle part.
It is known to mount a rotation detecting apparatus to detect the rotation of a wheel or crank arm so that a cycle computer may use the detected rotations to calculate and display the bicycle speed or pedal cadence to the rider. A conventional rotation detecting apparatus typically comprises a magnet mounted to a rotating part and a magnetic sensor mounted to a fixed part such as the bicycle frame. The magnetic sensor may comprise a reed switch, a Hall-effect element, etc., and it usually is mounted in a position that faces the magnet at some time during rotation of the bicycle part. For example, when used to calculate bicycle speed, the magnet may be mounted to the spoke of a wheel, and the magnetic sensor may be mounted to the front fork. When used to calculate pedal cadence, the magnet may be mounted to the crank arm, and the magnetic sensor may be mounted to either the seat tube or the down tube of the bicycle frame.
Only one magnet is mounted to the rotating part in a conventional apparatus, so the magnetic sensor outputs a detection signal one time for each rotation of the rotating part. Recently, the results of these detections have been used in gear control or suspension control. In such applications, there are instances when a detection cycle of one detection signal per rotation is inadequate to properly control the intended device. This is especially true when the rotating part is rotating at low speed, in which case the detection cycle is too long to adequately control a device that requires rapid response to changing conditions.
One attempt to solve this problem involves installing a plurality of circumferentially spaced magnets on the rotating part. For example, a plurality of magnets may be mounted to selected spokes of a wheel, thereby shortening the detection cycle and speeding up the response to the changing conditions. In such an apparatus, the plurality of magnets and the magnetic sensor must be mounted one by one to the rotating part. Furthermore, the circumferential spacing and radial position of the magnets must be adjusted one by one as they are mounted. Thus, the installation of the plurality of magnets and the magnetic sensor becomes troublesome. Even after the installation is complete, adjustment of the plurality of magnets or the magnetic sensor must be repeated whenever the plurality of magnets and/or the magnetic sensor shifts out of position due to the loosening of the mounting screws or the like.